Polyphenylene ether resins are high performance naturally flame retardant engineering thermoplastics having relatively high melt viscosities and softening points (i.e., in excess of 200.degree. C.). They are useful for many commercial applications requiring high temperature resistance and can be formed into films, fibers and molded articles. However, the art has recognized that polyphenylene ethers have a major drawback which is that they can not be easily melt processed and foam molded, particularly to very low densitites.
Polyphenylene ethers have been combined with polystyrene resins to improve moldability. For example, Cizek, U.S. Pat. No. 3,383,435, discloses that improved processability of polyphenylene ether can be obtained by addition of polystyrene and copolymers containing polystyrene includng rubber-modified high impact polystyrene.
More recently, Katchman et al., U.S. Pat. No. 4,128,602 disclosed using a polystyrene resin and rubber having a dispersed particulate rubber phase wherein the dispersed particles have a maximum mean diameter of about 2 microns to provide a polyphenylene ether resin having improved impact strength. Sugio et al., U.S. Pat. No. 4,448,931, disclosed a polyphenylene ether resin composition having improved impact resistance containing a rubber-modified polystyrene, wherein at least 80% of the rubber particles based on the total number of rubber particles in the elastomeric phase of the rubber-modified polystyrene resin have a particle diameter in the range of 0.5 to 4 microns and the elastomeric phase has a particle size distribution index (SDI) of no more than 1.9. Bennett and Lee, Jr., U.S. Pat. No. 4,513,120, disclosed a polyphenylene ether resin composition having improved impact strength and surface appearance containing a rubber-modified polystyrene, wherein a substantial majority of the rubber particles are of the core/shell type having a polystyrene core and a rubber membrane, and the particles are dispersed in a styrene matrix, the particle diameter being no greater than about 2 microns (average) and the particle size distribution (Sv/Sn) being above 3.20, e.g., 3.25.
Although the aforementioned compositions are stated to have improved impact strength, there is no disclosure in Sugio et al. of improvement in the gloss and no disclosure in either of the effect on flow properties of the polyphenylene ether compositions.
Applicants have now discovered a novel high impact polystyrene defined by the maximum mean diameter of the rubber particles and their particle size distribution which when used, either alone, or when combined with polyphenylene ether resins provides molded articles with high gloss, improved flow properties and vastly improved impact strength over known compositions.
It is therefore an object of the present invention to provide a novel rubber modified high impact polystyrene.
It is a further object of the invention to provide a polyphenylene ether resin/rubber modified high impact polystyrene composition having improved gloss, flow properties and impact strength.
It is a still further object of the invention to provide molded articles from the polyphenylene ether resin/rubber modified high impact polystyrene composition which are lightweight and have improved properties over molded articles made from known modified polyphenylene ether resins.